This invention relates to rechargeable or secondary batteries and, in particular, to secondary batteries using zinc negative electrodes.
Zinc negative electrodes of conventional secondary batteries (e.g., Ni--Zn, Ag--Zn, O.sub.2 --Zn, etc.) exhibit decay in usable capacity with repetitive charge-discharge cycling of the battery. As the battery and, therefore, each zinc negative electrode is cycled, there is a redistribution and densification of the electrode active material from the edges of the electrode to the electrode center. This results in a loss of surface area of the electrode active material with a concomitant loss of battery capacity.
Over the years, many different battery constructions have been proposed to reduce this zinc electrode "shape change". These different battery constructions have primarily involved attempts at modifying conventional monopolar batteries in which the battery electrodes and other components are vertically disposed in side-by-side relationship. However, these modified monopolar batteries have not been able to fully alleviate the factors believed to contribute to the zinc electrode shape change. These factors include the following:
1. Unequal current regions across the surface of the zinc electrodes which causes zinc active material to dissolve and replate unevenly. PA1 2. Electrolyte pH gradients causing uneven dissolution of zinc active material across the electrode surface. PA1 3. Electrolyte concentration gradients caused by gravity resulting in unequal zincate movement across the zinc electrode during charge and discharge.
It is, therefore, an object of the present invention to provide an improved zinc secondary battery.
It is a further object of the present invention to provide a zinc secondary battery in which cycle life of the battery is increased, while shape change of the zinc negative electrode is reduced.
It is yet a further object of the present invention to provide an improved zinc secondary battery which is sealed and maintenance free.